A memorial to Trayvon Martin sits outside The Retreat at Twin Lakes community where Trayvon was shot by George Michael Zimmerman while on Neighborhood Watch patrol on March 21, 2012 in Sanford, Florida. (Gerardo Mora/Getty Images)

(USA Today) -- The laws allow everyday citizens to use deadly force against someone else if they fear for their life. They also say people do not have to retreat if threatened or attacked.

George Zimmerman, a neighborhood watchman in Sanford, Fla., fatally shot Trayvon Martin as the 17-year-old was walking to his father's home from a 7-Eleven. Zimmerman says he acted in self-defense and has not been arrested or charged. Civil rights groups are calling for his arrest. Martin was black; Zimmerman is Hispanic.

The case has triggered a wave of public outcry to change or repeal Florida's "stand your ground" law.

"You want to know how you can kill somebody legally in Florida?" says Arthur Hayhoe, executive director of the Florida Coalition to Stop Gun Violence. "Make sure you have no witnesses, hunt the person down and then say you feared for your life."

Hayhoe says he has about a dozen cases on his desk now similar to Trayvon's case. He says in those cases, gunmen say they were defending themselves and have not been charged, leaving grieving relatives to wonder why the shooters have not been charged.

Florida's "stand your ground" law emerged after a man shot and killed a burglar who officials say was trying to break into the man's RV in the aftermath of Hurricane Ivan in 2005. The man waited months before learning he would not be charged with murder.

The case inspired then-Florida state senator Durell Peaden to introduce a bill dealing with similar situations. Florida state representative Dennis Baxley, the bill's House sponsor, told USA TODAY the law empowers people to defend themselves and should not be challenged in the wake of the Trayvon Martin case.

"Every time you have an adverse incident, immediately the anti-gun faction will say this law is the problem," Baxley said, adding that violent crime in Florida has dropped since its implementation. "As public policy, it is fulfilling its purpose and working well. The perpetrators know everyone has the right to defend themselves. I think that has been a strong deterrent."

Since the law was enacted in 2005, the number of justifiable homicides in Florida has skyrocketed, said state Sen. Oscar Braynon, who represents the area where Martin lived with his mother. In 2005, there were 43 such cases; in 2009, the last complete year available, there were 105, he said.

Nationally, justifiable homicides by private citizens have been slowly rising since 2005. The number in 2010, the last full year measured by FBI, showed 278 such killings, the most in 15 years. The FBI uses a more restrictive methodology than Florida, only counting those people who are slain during the commission of felony.

Baxley thinks the jump in justifiable homicides shows the law is working. "The perpetrator suffered instead of the person they were victimizing. That's what those numbers mean," he said.

Florida's "stand your ground" law cannot be amended, only repealed, he says. "The crux of the law is 'I felt threatened,' " he said. "If you fiddle with that, the whole law collapses."

Florida does not track or keep statistics on cases where someone uses a "stand your ground" defense, said Bill Eddins, president of the Florida Prosecuting Attorneys Association. Anecdotally, he said, based on speaking with prosecutors statewide, more people seem to use the defense.

"It's been great for defense lawyers," said Richard Rosenbaum, a criminal defense attorney in Fort Lauderdale. "It has helped a lot of people get off on self-defense that would have been found guilty before 2005."